Traditionally, detergent powders were produced by spray drying. However, the spray drying process is both capital and energy intensive and the products were quite bulky, having a relatively low bulk density.
The desire for powders with higher bulk densities led to the development of processes which employ mainly mixing, without the use of spray drying. These mixing techniques offer great flexibility in producing powders of various different compositions from a single plant, by post-dosing various components after an initial granulation stage. The resultant powders have fairly high bulk densities, which is desirable for some product forms. However, many of these non-spray drying techniques are unsuitable for production of powders over a wide bulk density range and in particular, for the production of lower bulk density powders.
One kind of process, which does not involve spray-drying, and which is capable of producing medium bulk densities between those of spray dried and other non-spray dried powders, involves use of a low shear granulator, usually a fluidised bed apparatus. Although fluidised bed granulation processes per se can give good control of bulk density, there can still be problems with poor dispensing of the resultant product.
The principle of adding a “layering agent” (usually, an aluminosilicate) in the final stage of non-spray drying mechanical granulating process for detergents is well known, for example as described in “Surfactants in Consumer Products”, Springer Verlag, 1987, pp 411–413. This reference mentions that it may be applied in a fluid bed drier.
JP-A-61 06990 describes that spray dried particles may be pulverized in a mechanical granulator and mixed with a liquid binder, wherein such a layering agent may be added.
Application of an aluminosilicate in the final stage of a process involving two mechanical mixer/granulator, followed by a fluid bed drier, is disclosed in EP-A-390 251.
Processes in which detergent granules are made by spraying liquid binder onto solids in a fluidised bed apparatus are known from many references, for example WO-A-98/58046, WO-A-98/58047 and WO-A-98/58048.
A process in which a pregranulation step is effected in a high or low spaced granulator followed by a secondary granulation step in a fluid bed granulator is described in WO-A-97/22685. Preferably, a “flow aid” may be added in the pregranulator. The list of possible flow aids does not include aluminosilicate. In two examples, LAS is formed by in situ neutralisation in the pregranulator, in which some zeolite is added.
WO-A-00/44874 discloses processes for making cationic detergent granules. In one variant, an aqueous cationic surfactant solution is mixed with a water-insoluble highly absorbing material such as an aluminosilicate to form agglomerates. The agglomerates are then dried in a drier such as a fluid bed drier.
We have now found that dispensing properties are significantly improved if most or all of an aluminosilicate component is added in a pregranulation step which is followed by a further granulation step in a low shear granulator such as of fluid bed type.